Apparatus and method for filling a ball grid array template

ABSTRACT

An apparatus and method for filling a ball grid array template is disclosed. The apparatus comprises a normally horizontal base plate with the ball grid array template being mounted onto the base plate at one end. A solder ball supply bin is slidably mounted over the surface of the base plate. The bin is enclosed on three vertical sides, while the fourth vertical side proximate the ball grid array template is a pivotable ball gate. At rest, the bin is located at an end of the base plate opposite to the template. When the base is tilted, the bin slides from its rest location to the other end of the base plate, so that it is positioned over the template, thereby allowing the solder balls to fill the locating holes of the template. The base is then rotated so that it tilts the opposite way, allowing the bin to return to its rest position. As the bin returns to its rest position, the ball gate sweeps any excess balls on the surface of the template back into the bin. The sensing device monitors the position of the ball gate. If the ball gate is in an open position, this indicates an abnormality in operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Patent ApplicationPCT/SG03/000246 filed 13 Oct. 2003, which claims priority of SGapplication 0206254-5 filed 14 Oct. 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to ball grid array (BGA) and inparticular, an apparatus and method for filling a ball grid arraytemplate with solder balls.

2. Description of the Prior Art

Ball grid arrays techniques are common nowadays for connectinghigh-density IC components onto circuit boards. U.S. Pat. No. 5,655,704,issued to Matsushita Electric Industrial Co., 12 Aug. 1997 discloses amethod of filling a template or a stencil with solder balls as asweeping bin passes over the template. However, such method is verysusceptible to solder ball damage by the design itself as well as due toprocess variability, contamination or foreign particle. As a result ofthe damage, subsequent process becomes not possible or the object ofsubsequent depositing the solder ball on the BGA package is notpossible.

FIG. 1 shows a conventional method of filling a BGA template with solderballs. The BGA template 1 is provided with a plurality of holes toreceive a plurality of solder balls 3. A ball bin 2 sweeps over andabove the template 1 and deposits the solder balls 3 into the holes onthe template 1. As this deposition of the solder balls 3 can happenanytime when the solder ball 3 and the hole are aligned, the depositionmay take place just as the ball bin 2 is about to reach the particularhole at which the solder ball 4 is just about to drop in. As shown inFIG. 1, this may result in the ball 4 being quashed by the bin 2.Another possible situation is when the solder ball 6 fails to properlyseat in the hole due to foreign matter 5. The bin 2 will shear off thetop of the solder ball 6.

FIG. 2 is a perspective view showing a solder ball mounting apparatusdisclosed in U.S. Pat. No. 5,655,704. As shown in the FIG. 2, the solderballs are deposited onto the substrate 10 through the stencil 7. Theflux dots 11 on the substrate hold the solder balls 9 in place. However,as these flux dots 11 are liquid paste, the volume or height of the dot11 may vary as in the case of flux dot 12, where there is excessiveamount. This causes the solder ball 13 to stick out of the stencil 7 andbe sheared off at the top as the solder ball bin 8 passes over the ball13. There can potentially be cases where there is not any flux dots andthe solder balls will drop lower than the usual height and the solderball 14 will be sheared by the bin 8.

U.S. Pat. No. 5,499,487, issued to Vanguard Automation, Inc., 19 Mar.1996 discloses an apparatus for placing solder balls in a ball gridarray. The apparatus comprises a wheel having an inner and an outerface, and the wheel being rotatable about a horizontal axis, means forattaching a ball grid array to the inner face of the wheel, means forattaching a tooling fixture to the outer face of the wheel in a positioncorresponding to that of the ball grid array, means for forming areservoir of solder balls at the bottom of the wheel, means forcontrollably rotating the wheel to move the tooling fixture through thereservoir in a manner to fill recesses in the fixture with solder ballsand to remove from the surface of the array any excess solder ballswhich are not occupying recessed, the inner and the outer faces beingseparated a distance to permit the tooling fixture to engage solderballs in the reservoir while ball grid array does not engage the solderballs.

U.S. Pat. No. 5,551,216 relates to a method and apparatus for filling aball grid array. The apparatus comprises a reservoir for solder ballsand a tooling plate with an array of holes for receiving solder balls.U.S. Pat. No. 6,276,598 relates to a method and an apparatus for ballplacement. The method and apparatus are particularly suitable fortransferring solder balls to a ball grid array package.

The methods disclosed in the above U.S. Pat. Nos. 5,499,487, 5,551,216,and 6,276,598 make use of free flow of solder balls 17 over tiltedtemplates 15 with or without vacuum suction at the holes receiving thesolder balls. This method does not prevent excess solder balls 18 andsolder balls 19 remaining on the surface of the template or around theholes due to either static forces, vacuum leakage at holes or foreignmatter which may be sticky like flux used in the attachment to thesubstrate. In these citations, subsequent operation whereby the ballpick head 16 or a ball grid array substrate 20 is advanced above thetemplate will result in quashed solder ball or multiple balls at eachhole in the pick head or at each electrode on the ball grid array (asshown in FIGS. 3 and 4).

U.S. Pat. No. 5,918,792, issued to RSVI Vanguard, Inc., 6 Jul. 1999,discloses ball grid arrays and method for placement of solder balls ontothe pattern of metallized pads or dots of such arrays. The apparatuscomprises an elongated holder defining an elongated recess therein forthe carrier of the array, a stencil overlying the recess and supportedby guide rails, a block of rigid material having a planar bottom surfacecontacting the stencil and for movement along the stencil, and means formoving the block along the stencil for moving a bin contacting solderballs over the apertures formed on the stencil for filling theapertures.

SUMMARY OF THE PRESENT INVENTION

Accordingly it is an object of the present invention to provide anapparatus and method for filling a ball grid array template with solderballs. Yet another object of the present invention is to provide anapparatus for filling a ball grid array template having locating holeswith a plurality of small solder balls comprising

a base plate rotatably mounted at the axis thereof to a controllingdevice and the ball grid array template being mounted onto the baseplate so that the template rotates simultaneously with the base plate;

a ball supply bin slidably mounted over the top surface of the baseplate while being rotated together with the base plate, the slidingmotion of the ball supply bin being controlled by a driving means suchas a motor, and the ball grid array template about the axis of the baseplate, and the ball supply bin being substantially rectangular andenclosed on three vertical sides while the fourth vertical sideproximity to the ball grid array template being a ball gate, said ballgate pivoted about the axis thereof and being normally rested by a stoppin or the like, such as a stopping edge, positioned at the lowersurface of the ball gate;

a sensing device positioned at both the ends of the base plate at aheight similar to the height of the ball gate from the base plate formonitoring the opened/closed position of the ball gate; and

a plurality of small solder balls enclosed by the ball supply binthereby when the base plate tilted towards the ball grid array template,the bin supply bin slides to and over the ball grid array template andthereby fill up the locating holes on the template with solder balls,the base plate is then tilted in the opposite direction, the ball supplybin slides back to the other end and simultaneously, the excess solderballs are fallen back with the supply bin.

Yet a further object of the present invention is to provide a method offilling solder balls on a ball grid array template having a plurality oflocating holes, said method comprising the steps of:

positioning said ball grid array template at one end of a pivotal baseplate;

introducing a plurality of solder balls in a ball supply bin which isslidably positioned at the one end of the base plate, and is slidable onthe base plate;

clockwise rotating of the base plate, causing the ball supply binsliding towards the ball grid array template to allow the solder ballscontained in the ball supply bin to fill the locating holes on thetemplate, and the sliding motion of the ball supply bin being controlledby a driving means such as a motor, each solder ball for each locatinghole; and

counter-clockwise rotating of the base plate and sliding of the ballsupply bin back to its initial position and, in so doing, remove anyexcess solder balls from above the ball grid array template.

A further object of the present invention is to provide an apparatus forfilling solder balls on a ball grid array template, further comprising aball pick head which is lowered above the ball grid template to removethe solder balls by vacuum for transferring to a ball grid arraysubstrate.

Yet another object of the present invention is to provide a method offilling solder balls on a ball grid array template, wherein the baseplate is tilted clockwise in an angle ranging from 5 to 40 degree abovehorizontal.

Yet another object of the present invention is to provide a method ofremoving excess solder balls from a ball grid array template, whereinthe base plate is tilted anti-clockwise in an angle ranging from 20 to75 degree.

An embodiment of the invention will now be described by way of exampleand with reference to the accompanying drawings, in which

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly enlarged cross-sectional view showing a conventionalsolder ball mounting apparatus.

FIG. 2 is a cross-sectional view of another conventional solder ballmounting apparatus.

FIGS. 3 and 4 schematically show instances which may result in quashedsolder ball or multiple balls at each hole in the pick head or at eachelectrode on the ball grid array in a conventional solder ball mountingapparatus.

FIG. 5 is a cross-sectional view showing the depositing of solder ballsfrom the ball supply bin to the ball array template in accordance withthe present invention.

FIGS. 6 to 15 are cross-sectional views showing operation sequence ofdepositing of solder balls in accordance with the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

While the specification concludes with claims defining the features ofthe invention that are regarded, it is believed that the invention willbe better understood from a consideration of the following descriptionin conjunction with the drawings.

Referring now to FIG. 5, there is shown an apparatus for filling solderballs on a ball grid array template in accordance with the presentinvention. The apparatus comprises a base plate 1 rotatably mounted atthe axis 2 thereof to a controlling device; a ball grid array template 3mounted onto the top surface of the base plate 1 at one end thereof sothat the ball grid array template 3 rotates simultaneously with the baseplate 1 when the base plate 1 rotates (tilts) clockwise oranti-clockwise; a ball supply bin 4 substantially rectangular shapeslidably mounted over the top surface of the base plate 1 at the otherend thereof and corresponding to the position of the ball grid arraytemplate 3 and the ball supply bin is driven by a motor and is moveablealong the base plate 1 while the base plate 1 rotates about the axis 2of the base plate 1. In accordance with the present preferredembodiment, the ball supply bin 4 is enclosed on three vertical sideswhile the fourth vertical side, proximity to the ball grid arraytemplate 3, is provided with a ball gate 5. The ball gate 5 is pivotedabout the axis 6 thereof and is normally rested by a stop pin 7positioned at the lower surface of the ball gate 5 when the base plate 1rotates clockwise or counter-clockwise. The ball grid array template 3is provided with a plurality of locating holes 12 on the top surface tohold solder balls 10, and one locating hole 12 receives only one solderball 10, as shown in FIG. 5.

A sensing device 8, such as a through-beam sensor, or a focused-beamreflective sensor is positioned and supported at both the ends of thebase plate 1 at a height similar to the height of the ball gate 5 fromthe base plate 1 for monitoring the opened/closed position of the ballgate 5. If the ball gate 5 is in an open position, this indicates anabnormality in operation. The ball gate 5 is designed in such a way thatthe weight of the ball gate 5 is pivoted about the axis 6 and the weightwill ensure that the ball gate 5 forms a close wall to contain thesolder balls 11 within the ball supply bin 4.

As shown in FIG. 5, a plurality of small solder balls (in bulk) 11 areenclosed by the ball supply bin 4. A ball pick head 9 is positionedabove the ball template 3 and is lowered to remove the solder balls 10on the ball grid array template 3 by vacuuming for transferring to a BGAsubstrate 19 (referring to FIG. 15).

In accordance with the present invention, a vacuum 18 is provided to achamber 13 underneath the ball grid array template 3, in communicationwith the individual locating holes 12 on the ball grid array template 3so as to assist the filling of the solder balls 10 (referring to FIG. 7and FIG. 8).

FIGS. 7 through 15 depict the operation of the apparatus in accordancewith the present invention.

At the initial operation of the apparatus, the base plate 1 togetherwith the ball grid array template 3 having no solder balls 10 on thelocating holes 12 are in the horizontal position (as shown in FIG. 6).As shown in FIG. 6, the solder balls 11 are contained within the ballsupply bin 4 and the ball gate 5 is at the close position.

Referring to FIG. 7, the base plate 1 tilts or is rotated clockwise toabout 5 to 40 degree above horizontal. The angle of rotation isdetermined by the ability of the solder balls 11 within the ball supplybin 4 to spread out towards the ball gate 5 to maximize ball depositionpossibility over the ball grid array template 3 in subsequent steps. Theball gate 5 forms a close wall to keep the solder balls 11 within thesupply bin 4.

As shown in FIG. 8, the ball supply bin 4 slides towards the ball gridarray template 3 and over the template 3 and in so doing, the solderballs 11 within the supply bin 4 are deposited into the locating holes12 on the surface of the template 3. The vacuuming means 18 connected tothe chamber 13 assist in filling the solder balls 10 into the locatingholes 12 on the template 3.

Referring to FIG. 9, the base plate 1 is then tilted or rotatedcounter-clockwise to about 20 to 75 degree below horizontal. Similarly,the angle of rotation is determined by the ability of the solder balls11 within the ball supply bin 4 to fall freely by gravity towards thefar-end of the bin 4 from the ball gate 5 and by the amount ofrotational torque balance at which the ball gate 5 is pivoted about theaxis 6.

Due to the fact that the solder balls 11 are typically very small, assmall as 0.2 mm diameter, some residual solder balls, denoted as 14, mayattach to the surfaces 15 of the base plate 1, the ball grid arraytemplate 3 or around the locating holes 12 due to static charges,humidity, contamination or vacuum leakage.

As shown in FIG. 10, at this angular orientation, the ball supply bin 4slides backwards and in so doing sweeps off excess residual solder balls14. The solder balls 10 deposited in the locating holes 12 remains inplace, held by either vacuum 18 in the chamber 13 or by the depth of thelocating holes 12.

1. A solder ball filling apparatus comprising: a base plate providedwith a ball grid array template on one end having a plurality oflocating holes extending therethrough for receiving solder balls, thebase plate having pivotal movement about a pivot between a first pivotdirection to move solder balls toward the ball grid array template and asecond, opposite pivot direction to move solder balls away from the ballgrid array template; a solder ball supply bin provided on the base platefor holding solder balls therein and for depositing solder balls in oneor more of the locating holes when the bin is located above the ballgrid array template; and a motor capable of moving the solder ballsupply bin along the base plate toward and away from the ball grid arraytemplate; wherein the solder ball supply bin comprises two oppositelydisposed side walls respectively connected by a rear side wall at oneend and a pivoted ball gate at an opposite end, wherein during pivotingof the base plate in the second direction, the ball gate pivots uponcontact with solder balls that have not moved away from the ball gridarray template.
 2. A solder ball filling apparatus according to claim 1,wherein the rear side wall is disposed at a distance relative to thepivoted ball gate such that when the bin slideably moves on the baseplate the rear wall does not slide over the ball grid array template. 3.The apparatus according to claim 1, further comprising a sensing devicepositioned at both the ends of the base plate, at a height similar tothe height of the pivoted ball gate from the base plate.
 4. Theapparatus according to claim 3, wherein the sensing device is athrough-beam sensor or a focused-beam reflective sensor.
 5. Theapparatus according to claim 1, wherein the base plate is pivoted at anangle ranging from 5 to 40 degrees in the first pivot direction.
 6. Theapparatus according to claim 1, wherein the base plate is pivoted at anangle ranging from 20 to 75 degrees in the second pivot direction. 7.The apparatus according to claim 1, wherein the locating holes in theball grid array template are in communication with a vacuum.
 8. A methodof filling a ball grid array template with solder balls, the ball gridarray template being provided on one end of a base plate and having aplurality of locating holes extending therethrough, the base plate beingcapable of pivotal movement between a first pivot direction and asecond, opposite pivot direction, and a solder ball supply bin beingprovided on a base plate that is capable of sliding thereon in the firstand second pivot directions, the method comprising: (a) providing solderballs in the solder ball supply bin; (b) pivoting the base plate in thefirst pivot direction to allow solder balls located in the bin to movein the first pivot direction; (c) moving the solder ball supply bin overthe base plate in the first pivot direction to the ball grid arraytemplate to thereby allow solder balls to fill one or more of thelocating holes; (d) pivoting the base plate in the second pivotdirection to allow solder balls located in the bin to move in the secondpivot direction away from the ball grid array template; and (e) movingthe solder ball supply bin over the base plate in the second pivotdirection; wherein the bin is capable of holding solder balls betweentwo oppositvely disposed side walls respectively connected by a rearside wall at one end and a pivoted ball gate at an opposite end, whereinduring step (e) the ball gate pivots upon contact with solder balls thathave not moved away from the ball grid array template.
 9. The methodaccording to claim 8, wherein the base plate is pivoted at an angleranging from 5 to 40 degrees in the first pivot direction.
 10. Themethod according to claim 8, wherein the base plate is pivoted at anangle ranging from 20 to 75 degrees in the second pivot direction. 11.The method according to claim 8, further comprising pivoting the baseplate to a horizontal position after step (e).
 12. The method of claim8, wherein the first pivot direction is a clockwise direction.
 13. Themethod of claim 8, wherein the second pivot direction is ananti-clockwise direction.